1. Field of the Invention
The present invention relates to a method for producing an acyl group-containing hexaazaisowurtzitane derivative which is useful as a precursor of a hexanitrohexaazaisowurtzitane derivative which can be used for improving the performance of conventional explosives. More particularly, the present invention is concerned with a method for producing an acyl group-containing hexaazaisowurtzitane derivative, which comprises: providing a composition system comprising a mixed solvent of a first solvent and a second solvent respectively having high and low dissolving abilities for the desired compound, wherein the mixed solvent has the desired compound dissolved therein; and (.alpha.) removing the first solvent having a high dissolving ability from the composition system to thereby deposit crystals of the desired compound, or (.alpha.') causing the above-mentioned composition system to undergo a phase separation into a first solvent phase containing the desired compound dissolved therein and a second solvent phase containing no desired compound or containing only a small amount of the desired compound dissolved therein, followed by removal of the first solvent from the first solvent phase to thereby deposit crystals of the desired compound.
The method of the present invention is commercially advantageous in that it can be used for producing an acyl group-containing high-purity hexaazaisowurtzitane derivative in high yield and at low cost.
2. Prior Art
As a conventional method for producing an acyl group-containing hexaazaisowurtzitane derivative, a method is known in which a hexakis(arylmethyl)hexaazaisowurtzitane is subjected to reductive dearylmethylation in the presence of an acylating agent to thereby obtain a hexaazaisowurtzitane derivative, which has an acyl group and having at least one type group or atom selected from the group consisting of an arylmethyl group, an alkyl group and a hydrogen atom, such as a tetraacylbis(arylmethyl)hexaazaisowurtzitane, a pentaacylarylmethylhexaazaisowurtzitane, a hexaacylhexaazaisowurtzitane, a tetraacyldialkylhexaazaisowurtzitane or a tetraacylhexaazaisowurtzitane (see "Tetrahedron" Vol. 51, No. 16, 4711-4722 (1995), and International Patent Application Publication No. WO 96/23792).
Further, hexaazaisowurtzitane derivatives are known which have an acetyl group, and a formyl group and/or an amino group (NH group) on a hexaazaisowurtzitane skeleton. Examples of such hexaazaisowurtzitane derivatives include a tetraacetyldiformylhexaazaisowurtzitane, a tetraacetylmonoformylmonoaminohexaazaisowurtzitane and a tetraacetyldiaminohexaazaisowurtzitane (International Patent Application Publication No. WO 97/20785).
In these patent and non-patent documents, as a method for isolating an acyl group-containing hexaazaisowurtzitane derivative, use is made of a method in which the reaction solvent is removed from the reaction mixture to obtain the desired compound as a solid, or a method in which the reaction solvent is removed from the reaction mixture to obtain the desired compound as a solid and the solid is then washed with an organic solvent.
However, these isolation methods for an acyl group-containing hexaazaisowurtzitane derivative have a problem in that a satisfactorily high degree of purification cannot be achieved and, hence, it is necessary to purify the isolated acyl group-containing hexaazaisowurtzitane derivative by subjecting it to recrystallization, so that not only does the production cost become high, but also the yield of the desired compound inevitably becomes low.